This invention relates generally to sensing systems and sensors, and, more particularly, to a sensing system with an array of grating-based fiber gas sensors that provide a measurement of a temperature-corrected gas concentration.
Power generating systems are being built today that have turbines using Syngas (hydrogen (H2) mixing with carbon monoxide (CO)) as fuel. The Syngas can be generated using a coal gasifier or other industrial processes. Also, gas turbines today can use a blend of Natural Gas (NG) and H2 fuel for power generation in order to obtain better operability, efficiency or emissions control. Typically, fuel streams used by turbines could contain Natural Gas (NG), which is primarily methane (CH4), diluents such as nitrogen (N2) and Carbon Monoxide (CO) and Carbon Dioxide (CO2), as well as higher molecular weight hydrocarbons, such as ethane (C2H6) and propane (C3H8). A hydrogen containing fuel could be a blend of low percentage of H2 in natural gas, or high percentages of H2 mixed with NG and/or other diluents, or a Syngas mixture, which is H2 with CO. For such applications, it becomes essential to monitor the composition of fuel that is being combusted so that its impact on output and efficiency of the turbines can be effectively controlled. Particularly, when H2-rich Syngas or NG blended with H2 is used as fuel for gas turbine, the fuel composition needs to be monitored online so that it can be controlled for required combustion performance driven by output, emission and efficiency requirement.
Existent H2 sensing technologies are largely unsuitable for direct online H2 concentration or composition monitoring due to several reasons. One reason is that, because of high concentration of H2, such conventional combustible gas sensors get saturated. Only spectroscope-based instruments, such as chromatography, mass spectrometer, Raman spectroscope, ring-down spectrometer, and the like, may be used for offline and not online H2 concentration or composition measurement. At the same time, the difficulty of deploying such bulky and dedicated spectrometry based sensors is obvious, especially, in harsh environments of coal gasifier and Syngas or natural gas combustors for real-time online monitoring/analysis of fuel quality. Although there are several conventional combustible gas sensors, such as infrared, electrochemical, metal oxide semiconductor based combustible gas-detection devices, they are either insensitive to hydrogen gas or saturated by high concentration or cannot be deployed in the harsh environments.
Other optical methods, such as fiber optic evanescent field-based, near infrared laser absorption, have been developed for H2-rich Syngas analysis. Usually, these gas-sensing devices require transparent medium and thermal sensitive optical parts installation. Thus, there is a need to provide a practical solution for online Syngas analysis for power generation performance in an environment such as gas turbine, combustor, and gasifier etc, as well as power generation efficiency control and optimization.